Initially, reference is made to the capacitive pressure transducer assemblies and circuitry shown in U.S. Pat. No. 4,388,668 granted Jun. 14, 1983, U.S. Pat. No. 4,398,426, granted Aug. 16, 1983 and U.S. Pat. No. 4,227,419, granted Oct. 14, 1980, all of which are assigned to the assignee of the present invention. In the transducers shown in these patents, a thin diaphragm of low hysteresis insulating material, such as a ceramic such as alumina, is employed; and when pressure is applied to the diaphragm it flexes toward an adjacent base member, normally of the same material, and conductive layers forming electrodes on the facing surfaces change their spacing, thereby varying the capacitance between the two conductive-layer electrodes. Circuitry included in the transducer converts the capacitance changes to an electrical signal varying linearly with the pressure changes. These pressure transducers are relatively inexpensive and have been widely used in automotive control and other applications.
Transducers for pressure ranges up to about 1000 psi have been made using substantially the arrangements shown in the above cited patents. However, at pressures substantially above 1,000 psi, corresponding to more than 60 or 70 atmospheres or bars, standard low pressure transducer configurations are not entirely practical, as the pressure seals and other components cannot handle the very high pressures.
An effective high pressure transducer operable up to about 10,000 psi, is disclosed in U.S. Pat. No. 4,617,607, granted Oct. 14, 1986, and also assigned to the assignee of the present invention. In that transducer the pressure is primarily absorbed by a relatively thick insulating diaphragm which is hermetically sealed outside of the high pressure fluid by means of a thin metal diaphragm which is substantially coextensive with and in contact with the thick insulating diaphragm, and welded or otherwise bonded to the fitting which includes the high pressure chamber connected to the source of high pressure fluid.
However, at the even higher pressures handled by the present transducer, the compressive strength of the ceramic insulating diaphragm may be inadequate; therefore, the type of high-pressure transducer based on the principles disclosed in U.S. Pat. No. 4,617,607 may not be entirely suitable for such high pressures without significant improvement. Such an improvement was disclosed in co-pending application of Ser. No. 08/057,541, assigned to the same assignee as the present invention.
Nevertheless, there remain possible improvements in the entire category of the transducers covered by all of the above-cited prior patents and co-pending patent application.
For example, it would be desirable if the manufacturing procedures required to produce the transducers were simpler and less expensive.
Finally it would be desirable if a single generic design were developed which was intrinsically adaptable by simple modifications to be applicable to any pressure in the range from low pressures to rather high pressures, bordering on ultra-high pressures.
Accordingly it is an objective of the present invention to attain simultaneously the following three desiderata:
1. inherent accuracy intrinsic to design; PA1 2. reduced complexity and cost of manufacture; PA1 3. adaptability to the entire range of low to ultra-high pressures.